All replies

What do you want it to pre-populate with, is it a static group that will be the same for each project, or a dynamic group that will change with each project. If static, you might be able to do something with Flow when the site is 1st created.

For existing groups, if you have a static set of users then again you might be able to do something with Flow and/or PowerShell.

Are you sure that it is the permission sync which is causing you perf issues and not something else?

So we are finding syncs are very slow, about 45 mins if syncing permissions via connected sites (per project). We are over both 1000 projects and 1000 resources, so this goes with Microsoft's recommendations to disable auto project permission sync. What
we want, is each time a new project is created, the site to be made (custom template) with some AD groups pre populated. This should be the same for every project, we run an open book policy (everyone can see everything)